1. Field of the Invention
The present invention relates to a strapping machine, in particular, it relates to a strapping machine adapted to be capable of automatically or semi-automatically conducting a procedure which includes looping a band made of a tape of a thermoplastic resin such as a polypropylene around an object to be strapped, and fusion-bonding an overlapping portion of the band to effect strapping.
2. Description of the Prior Art
To realize heightened efficiency and energy saving in a strapping operation, a strapping machine has already been practically used in general which is adapted to be capable of conducting a procedure that includes looping a band made of a thermoplastic resin tape around an object to be strapped, tightening the band, fusion-bonding the resulting nodally overlapping end portion of the band under heat and pressure, and cutting the band.
In such a conventional strapping machine, two-stage tightening is generally conducted as an operation for tightening a band, which comprises a primary tightening for high-speed/low-torque tightening of a band and a secondary tightening under low-speed/high-torque operation (see, for example, Japanese Examined Patent Publication No. 13205/1992).
Of the conventional strapping machines, a strapping machine has been known which is provided with an electric motor such as an induction motor for driving cams such as a press, a heater, a slide and the like for strapping with a band to cause timely shifted rotations thereof, and an electromagnetic clutch interposed between the electric motor and each of the cams, thereby intermittently controlling the driving force of the electric motor by means of the electromagnetic clutch (see, for example, Japanese Examined Patent Publication No. 69774/1991, and Japanese Unexamined Patent Publication No. 58613/1989).
In such a conventional strapping machine, there is a problem that when the electric motor such as an induction motor is stopped by being locked via the electromagnetic clutch, an undesired temperature elevation is inevitably caused due to electrical current continuously applied to the electric motor, and thereby failure of the driving means is likely to be caused. Consequently, durability is adversely affected, and cumbersome maintenance operations such as replacement and adjustment of parts is unavoidably required to be conducted frequently. There is a further problem that various equipments such as a power source for driving the electromagnet clutch and the like are required, thereby leading to a complicated structure with many equipments. This is, as a whole, disadvantageous in terms of cost.